System and method for vehicle performance control

ABSTRACT

A system and method are provided for controlling a drivetrain of a vehicle which includes a prime mover operatively connected to at least one tractive element. The system and method include determining the vehicle&#39;s total weight and, using an electronic controller carried by the vehicle, causing the prime mover to apply power to the tractive element so as to propel the vehicle. The magnitude of the power can be a function of the vehicle&#39;s total weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/503,466, which was filed on 15 Jul. 2009, and is titled “System AndMethod For Vehicle Performance Control,” the entire disclosure of whichis incorporated by reference herein.

BACKGROUND

The inventive subject matter described herein relates generally tomotorized vehicles, and more particularly to drive system performancecontrol in such vehicles.

Off-highway vehicles, such as mining trucks, are typically provided witha drivetrain in which an internal combustion engine drives a generatorthat provides electrical current to one or more traction motors. Offhighway vehicles typically also utilize dynamic or electric braking(referred to interchangeably herein as “retard effort”), in addition tohydraulically or mechanically operated service friction brakes.

Conventionally, mining trucks run at maximum available power up a grade,However, payload varies significantly from trip to trip, resulting inlarge variances in on-grade truck speed. This variance tends to cause aline of trucks to bunch up behind the truck with the heaviest load.

In conventional mining trucks, wheel torque is limited to a fixed valuewhich will give acceptable gear life over the overhaul cycle. Withlimited torque available, a mining truck with a heavy load can alsobecome stuck. A stuck truck is expensive for a mine, as it must bepulled out with a bulldozer, or have its load dumped so the truck can bedriven out empty. In either case there is lost production.

Conventionally, the maximum dynamic braking effort is set to apredefined curve as a function of speed. For a specific grade andpayload combination there is a maximum speed that the operator can driveand still maintain control of truck speed using only retard effort. Thisis known as the retard envelop. Once the truck exceeds the retardenvelop the driver must use friction brakes to slow the truck back intothe retard envelope. On many trucks the friction brakes are dry disksand have limited number of applications. The driver must keep vehiclespeed well within the retard envelope to insure he can maintain controlof the vehicle. This limits downhill speed and cycle time.

BRIEF DESCRIPTION

These and other shortcomings of the prior art are addressed by thepresently described inventive subject matter, which provides a systemand method for dynamically controlling the propulsion and brakingsystems limits of a vehicle.

According to one aspect, a method is provided for controlling adrivetrain of a vehicle which includes a prime mover operativelyconnected to at least one tractive element. The method includes: (a)determining the vehicle's total weight; and (b) using an electroniccontroller carried by the vehicle, causing the prime mover to applypower to the tractive element so as to propel the vehicle, the magnitudeof the power being a function of the vehicle's total weight.

According to another, a method is provided for controlling operation ofa drivetrain of a vehicle which includes at least one tractive elementcoupled to an electric traction motor, at least one electric energyabsorbing device coupled to the traction motor, and at least one powersource driven by a prime mover and coupled to the traction motor. Themethod includes: (a) using an electronic controller, causing thetraction motor to apply a predetermined baseline retarding force to thetractive element, and coupling the traction motor to the electric energyabsorbing device so as to dissipate the current generated thereby; (b)using the electronic controller, determining the vehicle's speed withreference to a retard envelope; (c) in response to the vehicle speedexceeding the boundaries of the retard envelope, applying an increasedretarding force to the tractive element; and (d) when the vehicle'sspeed has returned to the boundaries of the retard envelope, reducingthe retarding force to the baseline.

According to another aspect, a system for controlling a drivetrain of avehicle includes: (a) a prime mover coupled to a power source; (b) atleast one electric traction motor electrically coupled to the powersource, the traction motor coupled to at least one tractive element; and(c) an electronic controller operably connected to the traction motor,the controller configured to: (i) determine the vehicle's total weight;(ii) cause the traction motor to apply power to the tractive element soas to propel the vehicle, the magnitude of the power application beingproportional to the vehicle's total weight.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive subject matter may be best understood by reference to thefollowing description taken in conjunction with the accompanying drawingfigures in which:

FIG. 1 is a block diagram of a drive system for a vehicle constructed inaccordance with an aspect of the inventive subject matter; and

FIG. 2 is a schematic view of a driver control panel of the drive systemof FIG. 1.

DETAILED DESCRIPTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 depicts anexemplary drive system 10 for use in a vehicle “V”. The drive system 10includes a prime mover 12. In the illustrated example the prime mover 12is a Diesel engine, and the term “engine” may be used interchangeablywith the term “prime mover” throughout the remainder of thisdescription. The prime mover 12 drives an alternator 14. The output ofthe alternator 14 is converted into DC via a rectifier bank 16. The DCpower is provided over a DC bus 18 to an inverter unit 20. The inverterunit 20 includes DC-to-AC conversion circuitry of a known type, and alsoemploys components such as Insulated Gate Bipolar Transistors (IGBTs) orthyristors operating as pulse width modulators (not shown) to provide aAC power to a traction motor 22 which is coupled to a wheel 23 through aknown type of reduction gear (not separately shown). For the sake ofillustrative simplicity, only one inverter unit 20 and traction motor 22are shown, with the understanding that the vehicle V may be providedwith multiple traction motors 22 driven by multiple inverter units 20.

While an AC-DC-AC system is described herein, is should be noted thatthe principles of the inventive subject matter may be applied to otherdrivetrain configurations, e.g. using an alternator or DC generator as apower source, and using AC or DC traction motors. Furthermore, theprinciples of the inventive subject matter are also applicable to othertypes of vehicles, such as rail vehicles or road vehicles. The vehicle Vmay use any type of element adapted to exert a tractive force. Examplesof tractive elements include wheels, axles, or translating orreciprocating structures. The term “traction motor” could encompass, forexample, electric or hydraulic linear motors or actuators.

One or more chains of grid resistors 24 are connected across the DC bus18. The grid resistors 24 may be selectively coupled to the DC bus 18 todissipate power generated by the traction motor 22 and thereby providedynamic braking This is referred to as a “retard” function. Otherelectrical energy absorbing devices may be used in place of the gridresistors 24 to dissipate and/or use the power generated, for examplebatteries, a regenerative system, or equipment to use the power likeauxiliary systems and accessories.

The vehicle V includes at least one braking device 31 of a known type.The braking device 31 may be a service, parking, or emergency brake, andmay be hydraulically, mechanically, or electrically operated. Mosttypically, the vehicle V would include a service brake system plus anemergency or parking brake system.

A microprocessor-based controller 26 has operative connections to theengine 12, the grid resistors 24, the inverter unit 20, and to numeroussensors within the drive train, such as a wheel speed sensor 28 of aknown type coupled to the wheel 23. Among other functions, thecontroller 26 has the capability to control the speed of the engine 12,to command the inverter unit 20 to apply current to drive the tractionmotor 22 in a forward or reverse direction, to modulate the currentlevel supplied to the traction motor 22, and to connect the tractionmotor 22 to the grid resistors 24 through the inverter unit 20 to effectthe retarder function. In addition to the various discrete sensors, thecontroller 26 is provided with feedback from the inverter unit 20 whichis indicative of the magnitude of the torque being applied to thefraction motor 22. The controller 26 is also provided with means (i.e. aload cell) for determining the weight of a payload carried by thevehicle V. For example, the vehicle V may include a payload meter 33 ofa known type which computes total vehicle weight based on sensed airpressure in the vehicle's suspension struts 35. The payload meter 33 cancommunicate the total vehicle weight to the controller 26 over acommunications channel such as a serial bus.

A control panel 30, also referred to as a “driver information display”is coupled to the controller 26. As shown in FIG. 2, the control panel30 includes a display 32 for presenting information to the driver, andone or more controls 34 for operating the vehicle V. In the illustratedexample the display 32 is a multi-line LED, and the controls 34 areconfigured as a plurality of fixed and configurable keys. It will beunderstood that the control panel 30 could be configured differently,for example it could take the form of a touch screen interface. Inaddition to the control panel 30 the vehicle V also includes one or morediscrete vehicle controls operatively coupled to the controller 26, suchas accelerator pedal (not shown).

Optionally, the controller 26 may include means for two-waycommunication with a remote operator or dispatcher (see FIG. 1, shownschematically at 38). As illustrated the controller 26 is coupled to atransceiver 36 which communicates with the dispatcher 28 through awireless link.

The operation of the drive system 10 according to one aspect of theinventive subject matter will now be explained in more detail. In aregular driving mode in which traction motor torque is used to move thevehicle V, referred to as a “propel” mode, the controller 26 operatesthe vehicle to maintain one or more power targets which are a functionof the vehicle's weight. An example of a power target would be aspecific power loading, for example expressed as power output per ton.Another example would be vehicle speed, since the vehicle's speed isdetermined by its mass, rolling resistance, and the applied tractiveforce.

As an example, a known type of mining truck has an empty weight of about175 mt (193 tons), with an a Diesel internal combustion engine 12 ratedat about 2013 kW (2700 hp) and a maximum payload capacity of about 218mt (240 tons). When the operator depresses the accelerator pedal orotherwise commands vehicle movement, the controller 26 adjusts the loadon the engine 12. A separate engine controller (not shown) incorporatedwith the engine 12 adjusts fuel flow to the engine 12 to maintain agoverned RPM under load. The result is that the engine's output equals apower loading target which is below the maximum available power. As anexample, the target could be about 5.1 kW/mt (6.2 hp/ton). This wouldrequire about 1892 kW (2536 hp), or about 94% of maximum power if thepayload is about 90% of capacity. Alternatively, a target speed could beused, with the target speed selected being substantially below themaximum speed achievable at maximum engine output for a particularbaseline grade and payload.

The power target is “flat-rated” by a desired amount so that vehicleperformance is substantially equalized over a wide range. In thisexample, the target power loading of about 5.1 kW/mt (6.2 hp/ton) isequal to the loading at maximum payload capacity and thus could bemaintained, if desired, over the entire payload range of the vehicle V.The power target is a trade-off. A power target (speed or power loading)that represents higher engine output gives better acceleration andspeed, while a lower power target gives better consistency and alsoenables the desired performance to be maintained over a wider range ofpayload conditions.

The specific process used for control is not critical and may be carriedout by direct feedback control of vehicle speed, by using engine RPM asa proxy for power output, or by computation of actual torque and/orpower using signals from the inverter unit 20 or voltage and currentmeasurements from the DC bus 18. If the driver command for power outputis less than the power target (for example in reversing or in low-speedmaneuvering), then the supplied power would be equal to that commanded.The power target may be programmed in the controller 26 in various ways.For example, the power target could be manually entered into the controlpanel 30 by the driver. Alternatively, the power target could betransmitted to the vehicle V by the dispatcher 38.

In addition to variations in loading conditions, the power target isalso useful in accommodating variations in vehicle performance. Forexample, even when new, engines typically exhibit a +/−2% variation inperformance. As the vehicles 10 are used and age, there may besubstantial differences in performance from vehicle to vehicle. Thepower target can be used to limit multiple vehicles 10 to theperformance of the weakest vehicle V in the group. For example, if asequence of vehicles 10 about to make a trip is known, along with eachvehicle's total weight and maximum power, the dispatcher 38 may computeand assign a power target to each vehicle V, where the power targets arecalculated to obtain substantially equal speeds from each vehicle, andthereby prevent bunching of the group of vehicles. The power targetwould then be transmitted to each vehicle V.

The drive system 10 incorporates limits on the maximum torque output.Consistent with the prior art, this is done by limiting current flow tothe traction motors 22. Ordinarily, the maximum output will be set so asto provide acceptable overhaul life and margin against breakage ofcomponents such as the reduction gears. It is desirable to exceed theselimits occasionally, for example if the vehicle V should become stuckbecause of overloading or soft terrain. At low speeds, for example lessthan about 5.1 km/h (3.2 mph) for the vehicle described above,additional power is available from the engine 12. Accordingly, thecontroller 26 may be used to provide the vehicle with a temporary torqueboost when necessary. When such a boost is required, the controller 26commands the drive system 10 to temporarily provide extra torque to thewheels 23, by commanding the inverter 20 to increase its output.

The torque boost may be triggered by the driver, for example by enteringone or more commands in the control panel 30. A code or other securitymeasure may be used to prevent unauthorized requests. Alternatively, acommand to implement the torque boost may be transmitted from thedispatcher 38 to the controller 26 when boost is desired.

The boost usage may be limited in various ways to ensure that drivesystem life is not adversely affected. For example, the boost could belimited by amount of time per boost application, minimum time betweenapplications, maximum torque increase, total number of applications perday or per operating hour, or per overhaul cycle. It could also belimited to usage at specific times or geographic areas, or to when thevehicle payload exceeds a predetermined limit. The controller 26 maystore a data record of when, how long, and/or to what degree the torqueboost is used. This information may be used to adjust vehicle usage feesor maintenance fees, based on utilization.

The grid resistors 24 and associated hardware (also referred to as the“retard system”) have defined continuous heat rejection limits,expressed in kW or BTU/Hr. Given these limits, for a specific grade andpayload there is a maximum speed that the vehicle V can be driven andstill maintain control of vehicle speed using only dynamic braking(referred to interchangeably herein as “retard effort”). When themaximum speeds are mapped out for all grade and payload combinations,they represent the drive system's retard envelope. It is desirable tooperate the vehicle V as close as possible to the limits of thisenvelope, because it allows a higher average vehicle speed (and reducedtrip times) without increasing wear on the vehicle's friction brakingsystem. In order to facilitate operation close to the retard envelopelimits with high confidence, the controller 26 may be used to providethe vehicle V with a temporary boost in retard effort when necessary.

In order to accomplish this function, during retard operation, thecontroller 26 determines the actual retard effort being applied andcompares this to the retard envelope. This comparison may beaccomplished, for example, by using a software algorithm to examinevehicle acceleration and retard power and plot vehicle speed within theretard envelope. If the retard envelope is exceeded, for example ifmaximum continuous retard effort is applied, yet the vehicle speedcontinues to increase, the controller 26 increases the retard effortbeing applied beyond the continuous limit, in order to furtherdecelerate the vehicle V. The increased retard effort is held until thevehicle V is back within the normal retard envelope, by a predeterminedmargin. The magnitude of the margin is selected such that the finalvehicle speed is low enough that a reduced level of retard effort willmaintain the vehicle's speed, while simultaneously permitting thermalrecovery of the retard system.

Like the torque boost described above, the increased retard usage may belimited in various ways to ensure that drive system life is notadversely affected. For example, the boost could be limited by amount oftime per boost application, or minimum time between applications. Thecontroller 26 may store a record of when, how long, and/or to whatdegree the additional retard effort is applied. This information may beused to adjust vehicle usage fees or maintenance fees contractadjustment based on utilization.

The control system and method described herein has numerous advantagesover prior art vehicle drive systems. During propel operation, thevehicle V will have matched power to weight ratio for each load. Thiswill reduce the performance variation from vehicle to vehicle and loadto load—therefore reducing the tendency of vehicles to bunch up behindthe slowest vehicle. This allows the engine/drive system combination tooperate at the most efficient point as opposed to a driver trying toregulate speed following a vehicle ahead and going on and off thethrottle, wasting fuel. When full engine power is not required, thedrive system can lower engine speed as allowed to still provide thenecessary power. It also reduces the stress/temperature excursion onengine components. Temporarily boosting torque output when needed cangive the vehicle extra tractive effort to get unstuck when necessary,but limit reduction in component life by limiting applications. Finally,temporary boosting retard effort when needed allows an operator to driveat a higher speed closer to the edge of the retard envelope withconfidence of not losing control. This can result in improved vehicletrip cycle time.

The foregoing has described a method for vehicle performance control.While specific embodiments of the inventive subject matter have beendescribed, it will be apparent to those of ordinary skill in the artthat various modifications thereto can be made without departing fromthe spirit and scope of the inventive subject matter. Accordingly, theforegoing description of the inventive subject matter is provided forthe purpose of illustration only and not for the purpose of limitation,the inventive subject matter being defined by the claims.

What is claimed is:
 1. A method comprising: applying a retarding forceto a tractive element of a vehicle, the retarding force limited to nogreater than a predetermined baseline retarding force; responsive to thespeed of the vehicle exceeding one or more boundaries of a retardenvelope, applying an increased retarding force to the tractive element;and responsive to the speed of the vehicle being within the boundariesof the retard envelope, reducing the retarding force that is applied tothe tractive element to the baseline retarding force.
 2. The method ofclaim 1, wherein the retarding force is applied by a traction motor ofthe vehicle generating electric power.
 3. The method of claim 1, furthercomprising decelerating movement of the vehicle by maintaining theretard force that is applied to the tractive element, the movementdecelerated until the speed of the vehicle is within the one or moreboundaries of the retard envelope by at least a predetermined margin. 4.The method of claim 3, wherein the predetermined margin is sufficient topermit the speed of the vehicle to be maintained using the baselineretarding force that is applied to the tractive element.
 5. The methodof claim 1, wherein the one or more boundaries of the retard envelopeare based on heat rejection limitations on resistors that dissipateelectric power generated by a traction motor of the vehicle when thefraction motor applies the retarding force.
 6. The method of claim 1,wherein the one or more boundaries of the retard envelope are based ongrades being traveled upon by the vehicle.
 7. The method of claim 1,wherein the one or more boundaries of the retard envelope are based on apayload being carried by the vehicle.
 8. The method of claim 1, whereinthe one or more boundaries of the retard envelope are based on pluralcombinations of grades being traveled upon by the vehicle and payloadscarried by the vehicle.
 9. A system comprising: an electronic controllerconfigured to be operably connected to a traction motor of a vehicle,the controller configured to determine a total weight of the vehicle andto direct a traction motor of the vehicle to apply power to a tractiveelement of the vehicle so as to propel the vehicle, wherein thecontroller is configured to control the traction motor such that amagnitude of the power that is applied is proportional to the totalweight of the vehicle.
 10. The system of claim 9, wherein the totalweight includes a weight of payload being carried by the vehicle. 11.The system of claim 9, wherein the controller is further configured todirect the traction motor to apply a predetermined baseline retardingforce to the tractive element and to determine a speed of the vehiclewith reference to a retard envelope, the controller further configuredto, responsive to the speed of the vehicle exceeding one or moreboundaries of the retard envelope, direct the traction motor to apply anincreased retarding force to the tractive element and, responsive to thespeed of the vehicle returning to within the one or more boundaries ofthe retard envelope, direct the traction motor to reduce the retardingforce to the baseline retarding force.
 12. The system of claim 9,wherein the controller is configured to control the traction motor todecelerate movement of the vehicle by maintaining the retard force thatis applied to the tractive element until the speed of the vehicle iswithin the one or more boundaries of the retard envelope by at least apredetermined margin.
 13. The system of claim 12, wherein thepredetermined margin is sufficient to permit the speed of the vehicle tobe maintained using the baseline retarding force that is applied to thetractive element.
 14. The system of claim 9, wherein the one or moreboundaries of the retard envelope are based on heat rejectionlimitations on resistors that dissipate electric power generated by atraction motor of the vehicle when the traction motor applies theretarding force.
 15. The system of claim 9, wherein the one or moreboundaries of the retard envelope are based on grades being traveledupon by the vehicle.
 16. The system of claim 9, wherein the one or moreboundaries of the retard envelope are based on a payload being carriedby the vehicle.
 17. The system of claim 9, wherein the one or moreboundaries of the retard envelope are based on plural combinations ofgrades being traveled upon by the vehicle and payloads carried by thevehicle.
 18. A system comprising: an electronic controller configured tobe operably connected to a traction motor of a vehicle, the controllerconfigured to determine a weight of the vehicle and to direct a fractionmotor of the vehicle to apply power to a tractive element of the vehicleso as to propel the vehicle, wherein the controller is configured tocontrol the traction motor such that a magnitude of the power that isapplied is proportional to the total weight of the vehicle, thecontroller further configured to direct the traction motor to apply apredetermined baseline retarding force to the tractive element and todetermine a speed of the vehicle with reference to a retard envelope,wherein the controller also is configured to, responsive to the speed ofthe vehicle exceeding one or more boundaries of the retard envelope,direct the traction motor to apply an increased retarding force to thetractive element and, responsive to the speed of the vehicle returningto within the one or more boundaries of the retard envelope, direct thetraction motor to reduce the retarding force to the baseline retardingforce.
 19. The system of claim 18, wherein the weight of the vehicleincludes a weight of payload being carried by the vehicle.
 20. Thesystem of claim 18, wherein the one or more boundaries of the retardenvelope are based on at least one of heat rejection limitations onresistors that dissipate electric power generated by a traction motor ofthe vehicle when the traction motor applies the retarding force, gradestraveled upon by the vehicle, a payload carried by the vehicle, orplural combinations of grades being traveled upon by the vehicle andpayloads carried by the vehicle.